Numerous electrical circuits, for example, dc to dc converters, synchronous converters, and the like, require a number of semiconductor components, such as MOSFETs. These components typically generate heat which can increase the on-resistance or forward voltage drop of the MOSFET. If the MOSFET is located near other components, such as a microprocessor, the heat generated can also interfere with their operation.
Typically, the components are each housed in a surface mount package which normally consists of the semiconductor component die mounted with its back surface in contact with the surface of a lead frame and with its front surface including wires extending from connection pads to the lead extensions of the lead frame. The bottom of the lead frame is then typically located atop a heat-conducting slug whose bottom surface is to be connected to a flat surface which is to receive the surface mount package. The assembly, consisting of the die, lead frame and heat-conducting slug, is then encapsulated so that the flat bottom surface of the slug is exposed for surface connection and so that the lead frames extend out of the molded housing for external connection.
Surface mounted packages typically have a large plastic insulation portion located beneath the main pad area of the lead frame, namely between the lead frame and the board to which the device is mounted, that is unused. Also, the semiconductor device die is mounted to the top of the lead frame, which necessitates increasing the thickness of plastic at the top of the package to protect the die, thereby increasing the height of the package. It is also desirable to reduce the height of the surface mount package.
Principally, however, it is desired that heat be removed from the package as efficiently as possible.